Sonic Mega Collection is a compilation of past Sonic the Hedgehog video games repackaged by Sega for the Nintendo GameCube and released in November 2002 for a low price of $39.95. The set includes...

The games are direct emulated editions of the original classics and are not upgraded or tweaked as in past compilations such as Sonic Jam. The GameCube controller maps to the old Sega Genesis pad surprisingly well, with the control pad or the control stick used to control Sonic and friends while the old A, B, and C buttons have been mapped to B, A, and X respectively. The Z button stops the emulation of the game and offers a chance to exit, resume, or reset to the game's title screen. The L, R, and Y buttons do nothing during gameplay.

Rumors on video gaming sites have placed Sonic CD and a few other Sonic Team games in the set as hidden bonuses, so only time will tell if these prove to be accurate. For the record Sonic Team has denied that Sonic CD is on the set because the game took up too much space to be included and the Sega CD emulation was buggy and not up to the usual Sega standards. The confirmed hidden games are unlocked by playing the other games on the set a preset number of times and include...

The set also includes a Sonic Jam-esque collection of print artwork, game manuals, comic book covers, commercials, and other game media from the Sonic universe that is viewable onscreen. This collection includes game manual scans, Sonic comic book covers, and much more. In 2003 Sonic Team mastermind Yuji Naka claimed that Sonic Adventure DX could be considered Sonic Mega Collection 2 because it contains all twelve Sonic Game Gear titles as hidden bonuses. In 2004 an "upgraded" version of the collection was released for the Sony PlayStation 2 as Sonic Mega Collection Plus.


References:
http://www.sonicteam.com/sonicmega/index.html
http://www.gamefaqs.com